Hydrodesulfurization of heavy petroleum oil at higher temperatures and space velocities

ABSTRACT

Heavy hydrocarbon oils are desulfurized at high temperature and high space velocity in the presence of a catalyst comprising a Group VIII metal and a Group VI metal or their compounds and also containing as an agent for reducing the deactivation rate of the catalyst, a small amount of a Group VII metal or compound thereof.

United States Patent Kravitz et al. Oct. 28, 1975 HYDRODESULFURIZATION0F HEAVY 3,383,305 5/1968 Rogers et al 208/216 PETROLEUM OIL AT HIGHER3,598,725 8/1971 Hilfman 208/216 TEMPERATURES AND SPACE VELOCITIES [75]Inventors: Stanley Kravitz, Fishkill; Jitendra A. Primary ExaminerDelbert GantZ Patel Beacon; William Mather, Assistant Examiner-G. .1.Crasanakis Jr" Hopewell Junction a of Attorney, Agent, or FirmT. H.Whaley; C. G. Ries; 7 Robert Knox [73] Ass1gnee: Texaco Inc., New York,N.Y.

[22] Filed: Dec. 7, 1973 57 ABSTRACT [21] App]. No.: 422,630 1 Heavyhydrocarbon oils are desulfurized at high temperature and high spacevelocity in the presence of a 81.2 catalyst comprising a Group VIIImetal and a Group 58] Fie'ld 208/216 VI metal or their compounds andalso containing as an agent for reducing the deactivation rate of thecata- [56] References Cited lyst, a small amount of a Group VII metal orcomd th f. UNITED STATES PATENTS poun ereo 2,897,143 7/1959 Lester et a1208/216 13 Claims, N0 Drawings HYDRODESULFURIZATION OF HEAVY PETROLEUMOIL AT HIGHER TEMPERATURES AND SPACE VELOCITIES This invention relatesto the desulfurization of petroleum fractions. More particularly, it isconcerned with the catalytic hydrodesulfurization of heavy petroleumoils under conditions whereby the throughput and desulfurization of aunit may be increased and the hydrogen consumption in thedesulfurization procedure may be reduced with prolonged catalyst life.

The catalytic desulfurization of petroleum hydrocarbons has been wellknown in the refining industry for many years. It has been discussedquite thoroughly in Petroleum Processing Nov. 1956, pages 116-138. Theliterature discloses reaction conditions, using a fixed bed ofparticulate catalyst, in the broad ranges of temperatures of from400-900F., pressures of from 50-5000 psig, hydrogen rates of fromZOO-20,000 standard cubic feet per barrel (scfb) and space velocities of0.1- volumes of oil per volume of catalyst per hour /h Experience hasshown that in the commercial desulfurization of heavy oils such asvacuum gas oils and vheavier stocks, that is, oils having an initialboiling point of about 500F. or higher, using fixed beds andconventional desulfurization catalysts, the start-of-run temperatureusing fresh or freshly regenerated catalyst is preferably between about625 and 650F. and the end-of-run temperature about. 750F., a gradualincrease in temperature being made to compensate for loss of activity ofthe catalyst throughout the onstream period. Pressures range generallybetween about 500 and 1,000 psig with hydrogen rates of about 500-2,000scfb. Ordinarily in conventional commercial units the space velocity iscontrolled to obtain the desired amount of desulfurization with 85-90%desulfurization being considered as the most practical from anefficiency standpoint. For the most part, conventional commercial heavyoil desulfurization units are designed to operate at a space velocity ofabout I.

It has been generally accepted in the industry that hydrogen consumptionis a function of theamount of desulfurization and that as the percentagedesulfurization increases so does the amount of hydrogen consumed. It isalso a general belief in the industry that, other things being equal, adecrease in space velocity is required to obtain an increase indesulfurization. It has also been generally accepted that hightemperatures result in shortened catalyst life due to loss of activityon the part of the catalyst through deposition of carbon and in the caseof residue-containing charge stocks, metal-containing compounds on thesurface of the catalyst particles.

For ecological reasons, it has become necessary to refine more and morepetroleum fractions to reduce the sulfur content thereof thus makingdesulfurization costs enormous, not only in the amount of equipment thatmust be built but also in the costs of processing the various petroleumfractions such as the energy consumed in heating and pressurizing thepetroleum fraction and in the cost of hydrogen consumed. It has beenascertained that process improvements leading to a reduction in hydrogenconsumption of 100 scfb or an increase in desulfurization from 90-95% ora reduction in pour point of 40F. would result in a great economicimprovement over current operations. It would also be a distinctimprovement in the efficiency of a hydrodesulfurization unit if thecatalyst deactivation rate could be reduced thereby prolonging theonstream periods and reducing the overall down-time for catalystregeneration.

According to our invention, the efficiency of a desulfurization unit isimproved by contacting a sulfurcontaining petroleum oil having aninitial boiling point of at least about 500F. with added hydrogen at atemperature between 750 and 850F., a pressure between about 300 and 3000psig and a space velocity between 3 and 10 preferably from 4 to 8v/v/hr. in the presence of a hydrogenation catalyst comprising a GroupV] metal and an iron group metal or compounds thereof supported on arefractory inorganic oxide and containing from about 0.1 to 5% by weightof a Group VI metal such as manganese or rhenium based on the catalystcomposite.

Feeds which may be used in the process of our invention are heavypetroleum oil fractions having an initial boiling point of at leastabout 500F. and preferably at least 625F. Examples of feeds are gas oilssuch as vacuum gas oils, atmospheric residua, vacuum residua, heavycoker distillates, coal tar distillates and gas oils obtained fromshale, tar sand and the like. Generally, they contain from 0.5 to 5.0weight sulfur.

The hydrogen used in our process may be obtained from any suitablesource such as reformer by-product hydrogen, electrolytic hydrogen orhydrogen produced by the partial oxidation of carbonaceous orhydrocarbonaceous materials followed by shift conversion and CO removal.The hydrogen should have a purity of at least 50% and preferably atleast 65% by volume.

The catalyst used in the process of our invention v comprises a GroupVIII metal such as an iron group metal or compound thereof compositedwith a group VI metal or compound thereof on a refractory inorganicoxide support. Suitable Group VIII metals are particularly nickel andcobalt used in conjunction with tungsten or molybdenum. Preferably, themetals are in the form of the oxide or sulfide. Advantageously the riron group metal is present in an amount between about l.0 and 10% andthe Group VI metal is present in an amount between about 5 and 30% basedby weight on the catalyst composite. Examples of refractory inorganicoxides useful as supports are alumina, magnesia, zirconia and the likeor mixtures thereof. In a preferred embodiment the support is composedfor the most part of alumina stabilized with a minor amount, e.g. up toabout 5 wt. silica.

The catalyst also contains as an agent for reducing the deactivationrate of the catalyst, a small amount e.g., 0.5-5.0 preferably from0.2-2.0 percent of a Group VII metal e.g. rhenium or manganese based onthe weight of the catalyst composite. These metals or their compoundsare particularly effective in reducing the deactivation rate when thecatalyst is used at high temperatures such as 800-850F. and high spacevelocities such as 4-8 v/v/hr.

Neither the catalyst nor its preparation form any part of our invention.The catalyst may be prepared by conventional means such as thosedisclosed in US. Pat. No. 2,437,533 issued Mar. 9, 1948. The catalystmay be prepared by forming the support which, as mentioned above, is,for example, alumina containing a small amount of silica. The supportmay then be impregnated with the desired metals by use of a solution ofa water-soluble compound of the metal. For example, water solutions ofammonium molybdate, cobalt nitrate, nickel nitrate, ammoniummetatungstate, manganous nitrate or perrhenic acid may be used for theimpregnation. After the impregnation of the catalytic materials on thesupport, the composite is heated to dry and then calcined for severalhours in air at high temperature e.g., 900l000F. thereby converting themetals to the oxide.

The catalyst may be used as a slurry, a moving bed, a fixed bed or afluidized bed. In a preferred embodiment, the catalyst is used as afixed bed of particles which may be spheroids or cylindroids, the latterbeing preferred. When the catalyst is used as a fixed bed the oil flowmay be either upward or downward with concurrent hydrogen flow or theflow of oil may be downward counter to upwardly flowing hydrogen. In apreferred embodiment the hydrogen and the oil both pass downwardlythrough the fixed bed of catalyst particles.

In commercial installations it is customary to separate the hydrogenfrom the desulfurization zone effluent and recycle the separatedhydrogen to the desulfurization zone. To prevent the buildup ofimpurities such as low molecular weight gaseous hydrocarbons, hydrogensulfide and ammonia, a portion of the recycled hydrogen may be bled fromthe system and replaced with fresh hydrogen. Hydrogen may also be addedto the recycle stream to replace that consumed in the desulfurizationprocess. The ammonia and hydrogen sulfide may also be removed from thehydrogen by scrubbing with a methanolamine-water solution.

The following examples are submitted for illustrative purposes only andit should not be construed that the invention is limited thereto.

EXAMPLE I This example shows that the presence of rhenium in thecatalyst reduces the deactivation rate of the catalyst. The compositionof catalyst A is 3 wt. cobalt, 12 wt. molybdenum, 3 wt. silica and thebalance alumina. The cobalt and molybdenum are present as the oxides.The catalyst has a surface area of 290 m lg, a pore volume of 0.63 cc/gand an average pore diameter of 82.5A. Catalyst B is the same ascatalyst A except that it additionally contains 0.5 wt. rhenium. Thecharge stock is a West Texas-New Mexico vacuum gas oil having an APIGravity of 22 and a sulfur content of 1.85 wt. In each run the charge ispassed concurrently with hydrogen through a fixed bed of catalyst at theconstant conditions of 800F. 400 psig. 4 v/v/hr with 1,500 SCFB recyclehydrogen and 500 SCFB fresh hydrogen. The onstream period is reported interms of barrels of feed per pound of catalyst.

TABLE l-Continued Desulfurization Charge A These data show that there islittle difference in the initial desulfurization activity of thecatalysts but that the rhenium-containing catalyst loses its activity ata much slower rate.

EXAMPLE 11 Example I is repeated with catalyst C containing 3 wt.nickel, 13.6 wt. molybdenum and the balance alumina. Catalyst D issimilar to catalyst C but in addition contains 1.0 wt. rhenium. Thereaction conditions are the same as those of Example I.

These data show that the addition of rhenium to a nickel-molybdenum onalumina has substantially the same effect as its addition to acobalt-molybdenum on silicastabilized alumina.

They also show that the presence of rhenium is effective in slowing thedeactivation rate of the catalyst especially at a pressure below 500psig under which conditions catalysts used for the desulfurization ofheavy residuecontaining petroleum oils, that is, those having aConradson Carbon Residue of at least 1.0 wt are particularly susceptibleto rapid deactivation.

EXAMPLE III This is a substantial duplicate of Example II except thatCatalyst E contains 1 wt. manganese and the reaction conditions are800F., 350 psig, 6 v/v/hr. with a hydrogen circulation rate of 1,500SCFB recycle hydrogen and 500 SCFB fresh hydrogen.

TABLE 3 Desulfurization Charge C E TABLE S-Continued DesulfurlzutignThese runs show that at apressure of 350 psig, the deactivation rate ofCatalyst C is higher than in Example ll and also that the deactivationrate of Catalyst E is less than that of Catalyst C.

EXAMPLE IV This example is similar to Example I with respect to chargestock and reaction conditions,.the difference being that Catalyst Fcontains 2 wt. rhenium. As in the other examples, the time on-stream isreported in terms of barrels of feed per pound of catalyst.

A comparisonof this example with catalyst A of Example shows theeffectiveness of the addition of 2 wt. rhenium to the catalyst inreducing the deactivation rate of the catalyst at high temperature andlow pressure specifically a temperature of 800-850F. and a pressurebelow 500 psig.

Obviously, various modifications of the invention as hereinbefore setforth may be made without departing from the spirit and scope thereof,and therefore, only such limitations should be made as are indicated inthe appended claims.

We claim:

1. A process for the hydrodesulfurization of a petroleum oil fractionhaving an initial boiling point of at least about 500F. which comprisescontacting said fraction in the presence of added hydrogen underhydrodesulfurization conditions with a catalyst comprising an iron groupmetal, oxide or sulfide thereof and a Group V! metal, oxide or sulfidethereof on a refractory inorganic oxide support selected from the groupconsisting of alumina, magnesia and zirconia and mixtures thereof andcontaining between 0 and 5 wt. silica, said catalyst also containingfrom 0.1-5% by weight based on the catalyst composite of a Group V"metal or oxide thereof at a temperature between about 800 and 850F. anda space velocity between about 4 and 8 v/v/hr.

2. The process of claim 1 in which the hydrodesulfurization pressure isbelow 500 psig.

3. The process of claim 1 in which the Group Vlll metal is nickel.

4. The process of claim 1 in which the Group VIII metal is cobalt.

5. The process of claim 1 in which the Group Vl metal is molybdenum.

6. The process of claim 1 in which the Group Vl metal is tungsten.

7. The process of claim 1 in which the Group Vll metal is rhenium.

8. The process of claim 1 in which the Group Vll metal is manganese.

9. The process of claim 1 in which the petroleum oil fraction has aninitial boiling point of at least 625F.

10. The process of claim 1 in which the Group Vil metal is present in anamount between 0.2 and 2.0 wt.

11. The process of claim 1 in which the hydrodesulfurization pressure isabove 300 and below 500 psig.

12. The process of claim 1 in which the support comprises alumina.

13. The process of claim 1 in which the catalyst support is composed ofsilica in an amount up to about 5 wt. and the balance is alumina.

1. A PROCESS FOR THE HYDRODESULFURIZATION OF A PETROLEUM OIL FRACTIONHAVING AN INITIAL BOILING POINT OF AT LEAST ABOUT 500*F, WHICH COMPRISESCONTACTING SAID FRACTION IN THE PRESENCE OF ADDED HYDROGEN UNDERHYDRODESULFURIZATION CONDITIONS WITH A CATALYST COMPRISING AN IRON GROUPMETAL, OXIDE OR SULFIDE THEREOF AND A GROUP VI METAL, OXIDE OR SULFIDETHEREOF ON A REFRACTORY INORGANIC OXIDE SUPPORT SELECTED FROM THE GROUPCONSISTING OF ALUMINA, MAGNESIA AND ZIRCONIA AND MIXTURES THEREOF ANDCONTAINING BETWEEN 0 AND 5 WT. % SILICA, SAID CATALYST ALSO CONTAININGFROM 0.1-5% BY WEIGHT BASED ON THE CATALYST COMPOSITE OF A GROUP V11METAL OR OXIDE THEREOF AT A TEMPERATURE BETWEEN ABOUT 800* AND 850*F ANDA SPACE VELOCITY BETWEEN ABOUT 4 AND 8 V/V/HR.
 2. The process of claim 1in which the hydrodesulfurization pressure is below 500 psig.
 3. Theprocess of claim 1 in which the Group VIII metal is nickel.
 4. Theprocess of claim 1 in which the Group VIII metal is cobalt.
 5. Theprocess of claim 1 in which the Group VI metal is molybdenum.
 6. Theprocess of claim 1 in which the Group VI metal is tungsten.
 7. Theprocess of claim 1 in which the Group VII metal is rhenium.
 8. Theprocess of claim 1 in which the Group VII metal is manganese.
 9. Theprocess of claim 1 in which the petroleum oil fraction has an initialboiling point of at least 625*F.
 10. The process of claim 1 in which theGroup VII metal is present in an amount between 0.2 and 2.0 wt. %. 11.The process of claim 1 in which the hydrodesulfurization pressure isabove 300 and below 500 psig.
 12. The process of claim 1 in which thesupport comprises alumina.
 13. The process of claim 1 in which thecatalyst support is composed of silica in an amount up to about 5 wt. %and the balance is alumina.